You're barking up the wrong tree. When the ajnabi person someone's dating trashes the counterparts of their significant others' ethnicity, best believe s/he's trashing them to her/him lol. This often happens when the guy or girl for whatever reason hates, or has had negative dating experience (s) within their ethnicity, so when they eventually date out they either actively or passively defame the collective opposite sex of their background and the ajnabi picks up on that, and depending on their character, does the same.
In a normal, healthy relationship when you're dating an Ajnabi person you love, you attempt to venerate each other's cultures and ppl a bit...not this. Honestly they should've just let it go. Ppl need to leave ppl to themselves.